Today the main raw material to produce paper is wood. Its chemical composition in percentage looks like this: 44,2% of oxygen, 49,5% of carbon and 6,3% of hydrogen. Besides this in the wood there is a series of organic substances like lignin, hemicellulose, cellulose, resins, tanning materials, and not organic elements: kalium, calcium, magnesium, sodium.
There are over 400 types of paper that differ by composition, density (with the mass 1 m²), durability, smoothness, whiteness, color or shade, level of opacity, thickness, void content, field of application and, of course, price.
It’s possible to consider that process of paper production starts with wood cut. Untreated logs go to manufacture where first of all they go through tumbling barrel in which they dash and rub. Thus bark is removed and it is not thrown away, bark is gathered and used as a fuel. Clear logs are sent into cut machine to make chipped wood.
Chip is turned into wooden pulp by washing and alkaline treatment. Then it is put into big containers called boiling pots and there under pressure and temperature the pulp is turned into oatmeal-like wood pulp.
In special towers for alkaline treatment wood pulp is made white by processing with chemicals. Undesired components are removed and freed wood fibers form suspended material in a proportion about one part of fiber on 200 parts of water. It is the necessary extent of pulp dilution from paper density, fiber type and extent of pulp grind. This so called “composition” of paper goes through a cycle of processing on paper-making machine where it is partly dewatered. The concentration of water in wood pulp reduces from 95% to 5% after the processing in paper-making machine.
Paper-making machine is a multisection unit several meters long, comprised of separate sections in which paper web is formed consistently. It consists of: paper-machine feed vat for paper pulp accumulation and its feed to the equipment for pulp refinement, grind and clearing; water pumps, vacuum pumps for dewatering, units for rejects recycling, pools for reverse volume of water, combined extract and input ventilation, regulating and controlling-measuring devices. Paper pulp from vat is poured into a net with the help of air-cushioned inlet that provides uniform speed of feed and its uniform quantity along the whole width of the net. Paper web is formed while water is removed from fiber mass.
After vacuum the web goes through stage of mechanical dewatering passing between tightly pressed rolls one of which is covered with cloth. The cloth preserves paper structure from spreading during the pressing and moisture pickup. The final deletion of moisture happens through evaporation on two layers of drying cylinders arranged in chess-board order. Number of cylinders depends on the type of produced paper and paper-making machine speed. For example, in order to produce newspaper and bag paper usually 50-80 cylinders are used. In order to fix paper fibers and prevent extra absorption of ink during printing, the paper is treated with glue solution, and for better glossyness, smoothness and volume mass it goes through calender press. Quality characteristics of paper sheet are checked with the help of different analyzers.
When paper is ready it is rolled into huge reels or drums, which mass can reach 35 tons and length – 60 km. Part of reels are rerolled and cut into rolls with smaller width – they go to the clients, other part is cut into sheets and packed in piles. Before paper is packed its quality is checked one more time.
Modern paper-making machines are able to produce 2 km of web up to 10 m width within 1 minute. Within a year one machine can produce up to 400 000 tons of paper web. Machines differ by width and other technical characteristics depending on the type and technical characteristics of paper they produce. At Mondi Syktyvkar operate 3 paper-making machines and 1 cardboard-making machine.